Optical encoders are present in numerous electronic devices. They are employed to allow a user to input data. There exist, for example, rotary encoders comprising a rotating button driving a disk bearing alternating scattering and absorbing zones. The encoder also comprises a circuit board on which an emitter and a light sensor are positioned. The emitter, such as a light-emitting diode for example, emits light radiation in the direction of the disk. The sensor makes it possible to detect the light radiation when it is reflected by a scattering zone. It is thus possible to obtain, as output from the sensor, a binary signal that is representative of a reflection from a scattering zone, or of the absence of reflection when the light radiation strikes an absorbing zone.
A user manipulates the button in order to make the disk turn, thereby placing on the optical path between the emitter and the sensor either a scattering zone or an absorbing zone.
The protection of an electronic device from electromagnetic interference is always tricky to achieve. The use of metal walls that are electrically connected to a ground makes it possible to produce a shielding screen that isolates the device from its electromagnetic environment. However, when the device comprises movable portions such as those used to input of data into an encoder, the shielding screen is interrupted in order to allow for the passage of a movable part between the interior of the device, where, for example, a printed circuit board might be found, and the exterior of the device, where the movable part forms a member that is manipulated by a user.